Trays delivering loosely coherent boards of cellulosic and thermosetting material, to be cured under heat and pressure to form so-called fiberboard or chipboard plates, remain with their load in a platen press during the curing operation and are correspondingly heated on leaving the press. In order to enable such trays to be quickly ready for re-use, they must be suitably cooled before passing again through a loading station on their way to the press. Such cooling can be done in air with the aid of a slow-moving rack receiving the empty trays and carrying them over a predetermined path to a point of discharge. With proper synchronization between the movement of the rack and the operation of the platen press, as well as the various conveyors carrying the trays in a closed circuit through the press and the rack, no manual intervention of an operator is necessary anywhere in the cycle.
In such systems, however, the required unloading of each tray on its approach to the rack introduces the complication since additional structure is needed for gripping the hot boards, generally with the aid of suction cups, and depositing them on an ancillary conveyor as the trays move toward the cooling rack.